In recent years, frequency equalization single-carrier transmission systems have been studied with an eye toward next-generation mobile communication systems. In a frequency equalization single-carrier transmission system, data symbols arranged in the time axis direction are transmitted by a single carrier. A receiver corrects signal distortion in the transmission path by equalizing that distortion on the frequency axis. More specifically, the receiver calculates a channel estimation value for each frequency on the frequency axis, and performs weighting for equalizing propagation distortion on a frequency-by-frequency basis. Then the received data is demodulated (see Non-patent Document 1, for example). Therefore, in this system, there is a strong demand for a technology that will improve the precision of per-frequency channel estimation.
Generally, in a conventional frequency equalization single-carrier transmission system, slots on the time axis are defined as pilot slots that are used to perform per-frequency channel estimation value calculation, as shown in FIG. 1. Known pilot symbols for each frequency are then transmitted in the pilot slots.
With the OFDM (Orthogonal Frequency Division Multiplexing) method, in which data symbols are arranged in the frequency axis direction and transmitted by multiple carriers, a known pilot symbol is transmitted for each subcarrier actually used in radio transmission.
With OFDM, a technology called “scattered pilots” has been proposed as a technology for improving the precision of channel estimation. With scattered pilots, a pilot symbol is transmitted on one of the subcarriers on the frequency axis (see Non-patent Document 2, for example).    Non-patent Document 1: “Frequency Domain Equalization for single-Carrier Broadband Wireless Systems”, IEEE Communications Magazine, April 2002, pp. 58-66    Non-patent Document 2: “Channel Equalisation for OFDM Using Scattered Pilots”, Chen, N., Heaton, R., Tanaka, M., Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th, Volume 2, 6-9 May 2002 Pages 1040-1044, Vol. 2